def posterize(picture):
    #loop through the pixels
    for p in getPixels(picture):
        #get the RGB values
        red = getRed(p)
        green = getGreen(p)
        blue = getBlue(p)

        #check and set red values
        if(red < 64):
            setRed(p, 31)
        if(red > 63 and red < 128):
            setRed(p, 95)
        if(red > 127 and red < 192):
            setRed(p, 159)
        if(red > 191 and red < 256):
            setRed(p, 223)
        if(green < 64):
            setGreen(p, 31)
        if(green > 63 and green < 128):
            setGreen(p, 95)
        if(green > 127 and green < 192):
            setGreen(p, 159)
        if(green > 191 and green < 256):
            setGreen(p, 223)

    #check and set blue values
        if(blue < 64):
            setBlue(p, 31)
        if(blue > 63 and blue < 128):
            setBlue(p, 95)
        if(blue > 127 and blue < 192):
            setBlue(p, 159)
        if(blue > 191 and blue < 256):
            setBlue(p, 223)